The present invention relates to rock drilling tools and particularly to cross-impact rock drilling tools.
A cross-impact rock drilling tool in the prior art employs a central pilot shaft with a cutting member at its tip and cross-shaped arms protruding outward from the pilot shaft with cutting members at their ends. Such drills are reciprocated in a drill hole while also being rotated. The cutting member on the pilot shaft bores a pilot hole while the cutting members at the ends of the arms spaced radially outward from the pilot shaft crush a ring of rock. The annular ring of rock between the pilot hole and the crushed ring is crushed by impact with the arms.
When drilling upward, both large and small particles of crushed rock can fall through the spaced between the arms onto the face of the person holding the drill. When drilling downward, fine rock particles accumulate in the hole and cushion the impact of the drill and thus impair drilling effectiveness. In addition, the manufacture of cross-impact drills employing a plurality of radial arms is relatively expensive.